The objective of the proposed research is to elucidate mechanism of antidiurectic hormone (ADH) action on the kidney tubules in health and in disease. Special emphasis will be focused on the question how cyclic AMP formed in the cells of collecting tubules (CT) and ascending Henle's loop (ALH) regulates water permeability and chloride transport in these two tubule segments. The basis of these studies is the hypothesis that cAMP activates protein kinase which in turn modifies in a specific way the ultrastructure of membranes leading to change of water permeability in CT or increases NaCl transport in ALH. The specific objective is to determine direct or indirect factors which regulate cyclic AMP levels in CT and ALH and activation of protein kinase. It will be examined whether activation of protein kinase is essential for ADH action on membranes in CT and ALH, or on other target systems for protein kinase action in these tubules. Specific biochemical steps, similarities and differences between regulatory action of ADH on water permeability in CT and NaCl transport in ALH will be defined and compared. Special attention will be paid to development of a method for isolation and studies of luminal plasma membranes in CT and in ALH. Most of the studies will be performed on specific tubule segments (CT, ALH) microresected from animal kidneys. Enzyme activities, substrates, cofactors, activators and inhibitors of ADH sensitive-cyclic AMP system will be studied in dissected CT and ALH. Investigation will be conducted in kidneys of normal animals as well as kidneys of animals with inherited or drug-induced nephrogenic diabetes insipidus in search for elucidation of the pathogenesis of concentrating defects which are dependent on ADH action in this disease.